Initial boiling point analyzer



Jan. 28, 1964 Filed March 17, 1961 INITIAL BOILING POINT ANALYZER 2 Sheets-Sheet 1 Recording Vent - l2 i I0 55 E i i e To 4 A.C. Pwr. Source Feed (Sample) 2 Waste Out Potentio mejer Fig.

PRIOR ART -Goo|ing Liquid Out cooling Liquid In Water Out 7 30 A 1-32 Feed (sum 8) Feed and Reflux Out- To Member A and Boiler INVENTOR. CONAR D K. DONNELL BY MM??- w ATTORNEY Jan. 28, 1964 c. K. DONNELL 3,119,250

INITIAL BOILING POINT ANALYZER V Filed March 17, 1961 2 Sheets-Sheet 2 Recording Pofe niiornetgr Fig. 2 4

CONARD K. DONNELL Ou i BY Wm. 3 a

ATTORNEY United States Patent 3,119,250 INITIAL BOILING POINT ANALYZER Conard K. Donnell, Springfield, Pa., assignor to Sun Oil gornpany, Philadelphia, Pa., a corporation of New ersey Filed Mar. 17, 1961, Ser. No. 96,479 8 Claims. (Cl. 73-17) This invention relates to a boiling point analyzer, and more particularly to an analyzer which operates to record continuously the initial boiling point of a liquid stream.

A number of analyzers have been devised to record continuously the boiling point of a liquid hydrocarbon stream. In a petroleum refinery, continuous indication (recordation) of boiling point permits closer control of distillation columns, by providing the still operator with immediate notice of deviations from the desired properties in the various streams.

It is often desirable to determine the initial boiling point of a hydrocarbon stream. At least two analyzers are available commercially to determine the initial boiling point of such a stream. However, both of these instruments are upset by small amounts of water such as are usually present in refinery streams. These analyzers operate erratically, because they tend to record the boiling point of Water as the initial boiling point of the stream, although the actual initial boiling point of the water-free sample may be much higher.

An object of this invention is to provide a novel initial boiling point analyzer.

Another object is to provide a novel initial boiling point analyzer which operates in a continuous manner.

A further object is to provide an analyzer which will operate effectively even with a wet sample, the analyzer functioning to record the initial boiling point of the sample, without any interference from the water in the sample.

The objects of this invention are accomplished, briefly, in the following manner: The liquid hydrocarbon sample is boiled in a boiler, a thermocouple being used in the vapor space above the liquid to detect the desired temperature. A continuous water separator is incorporated with the boiler, the sample (feed) entering this separator first and thence flowing into the boiler. The water separator eliminates water present in the feed. Vapor from the boiler is condensed by means of a condenser associated with the water separator, the arrangement being such that the condensate flows to the water separator, from whence it flows to the boiler along with the new feed.

A detailed description of the invention follows, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic representation, mainly in longitudinal cross-section, of a typical initial boiling point analyzer according to the prior art;

FIG. 2 is a schematic representation, mainly in longitudinal cross-section, of an initial boiling point analyzer according to this invention; and

FIG. 3 is a partial view similar to FIG. 2, but illustrating a modified construction.

Referring first to FIG. 1, this figure illustrates a commercially-available analyzer using a simple reflux still to determine the initial boiling point. A sample of the wet liquid hydrocarbon stream to be analyzed is fed continuously (as by means of a pump) into a heated distillation vessel or boiler 1 by way of a conduit 2 opening into a tubular member 3 which extends downwardly from the base or bottom closure 4 of vessel 1 and which communicates at its upper end with the interior of vessel 1. The boiler 1 is heated by a cartridge-type immersion heater 5 which is supplied with electric current from a suitable source of alternating current power, such as a power line (not shown). A constant liquid level is maintained in boiler 1 by means of a metallic overflow line 6 Whose upper end opens into the boiler at a point above the bottom 4 thereof. Line 6 is of smaller diameter than tubular member 3 and is mounted concentrically thereof. Line 6 is sealed through the bottom end of member 3 and extends to a suitable waste or slop connection. The arrangement 3, 6 constitutes a heat exchanger, whereby the feed, flowing around the outside of line 6, is preheated (by the hot waste liquid in line 6) on its way to boiler 1.

The liquid 10 in boiler 1 is heated (by heater 5) so that it boils gently, thereby producing some vapor. The upper part of vessel 1, which is made for example of glass, is provided with a surrounding jacket 7 through which a cooling liquid e.g., water) is circulated by means of the hose couplings 8 and 9 provided at the upper and lower ends, respectively, of jacket 7. The arrangement 7-9 comprises a water-jacketed condenser which operates to condense the vapor produced by the boiling of liquid 10, the vapor condensing on the upper portion of the inner wall of vessel 1 and from thence flowing back down to the boiler. In other words, the condensed vapor is refluxed to the boiler.

A vent tube 11 communicates with the interior of vessel 1, above the jacket '7. This tube, which is open to the atmosphere at its outer end, ensures that the operation is carried on at atmospheric pressure.

A thermocouple 12, to which is connected a pair of electrical leads 13, is positioned in the vapor space above liquid 1%), just below the water jacket '7. Leads 13 extend upwardly to the top of vessel 1, and out through a suitable seal (not shown) to a recording potentiometer 14. Thermocouple 12 thus is used to record a vapor temperature in vessel 1. The position of the thermocouple 12 is critical, but at the proper location of this thermocouple the temperature recorded thereby will be equal to the initial boiling point of the sample as determined by Method D-86 (a batch procedure) of the American So ciety for Testing Materials (ASTM).

When the apparatus of FIG. 1 is used with a wet plant sample, small amounts of water (even that dissolved in the feed) are vaporized in the boiler and collect on the cold condenser surface (i.e., the upper portion of the inner wall of vessel 1), accumulating there until large enough drops are formed to reflux into the boiler. With the boiler at a relatively high temperature, the liquid water flashes violently when it reaches the boiler, depressing the vapor temperature (in vessel 1) momentarily to the boiling point of water, and usually causing violent foaming of the boiler contents. Several minutes may be required to recover from this condition before smooth operation is resumed, this smooth operation then occurring only until the water refluxes again.

In an actual test run, a wet plant sample (stream) of kerosene was fed to the boiler of a commercial analyzer such as shown in FIG. 1. Such a stream may have an initial boiling point on the order of 385 to 400 F. During a run of several days with this analyzer, the recorded vapor temperature repeatedly decreased, suddenly, as much as F. These decreases occurred at least every two hours, and sometimes as often as every five minutes. As much as thirty to forty minutes was required to recover from a severe upset, so that the aver-age record was extremely erratic.

Attempts have been made, in the past, to remove the water from the feed, and to remove the water accumulation in the stillhead (the upper, condsensing portion of vessel 1). However, these attempts have been only partially successful.

Refer now to FIG. 2, which illustrates an initial boiling point analyzer according to this invention. Speaking in general terms, in FIG. 2 a continuous water separator is incorporated with a boiler, in order to eliminate water present in the primary feed to the boiler; also, the reflux to the boiler is made to pass through this water separator.

In .FIG. 2 a vessel, denoted generally by numeral 15, has substantially the shape of an inverted U, with two vertically-disposed legs 16 and 17 joined at their upper ends by a horizontally-disposed arm 18. Vessel may conveniently be formed from glass. Some distance above the lower end of leg 17, a side tube or conduit 19 communicates with the interior of this leg, tube 19 having a branch portion 20 which extends downwardly and another branch portion 21 which extends upwardly and which opens to the atmosphere at its upper end. Some distance below the upper end of branch 21, a tube or conduit 22 communicating with this branch extends horizontally for a small distance, then downwardly and again horizontally to open into a tubular member 3 which extends downwardly from the base or bottom closure 23 of the vessel leg 16. Member 3 communicates at its upper end with the interior of vessel leg 16.

Vessel leg 16 may be thought of as a boiler, since it is heated by a cartridge-type heater 5 which is supplied with electric current from a suitable source of alternating current power, as in 'FIG. 1. A constant liquid level is maintained in vessel leg 16 by means of a metallic overflow line 6. 'Line 6 is mounted concentrically of tubular member 3. Again, the arrangement 3, 6 constitutes a heat exchanger, whereby the feed (liquid stream to be analyzed, which flows into boiler leg 16 by way of tube 22 and member 3, as will later be explained), flowing around the outside of line 6, is preheated (by the hot waste liquid in line 6) on its way to boiler 16.

A sample of the 'wet" liquid hydrocarbon stream to be analyzed is fed continuously (as by means of a pump) into the water separator leg 17 by way of branch 20. As the liquid hydrocarbon (which may contain free water) proceeds upwardly along line 20, it reaches the junction of tubes 20 and 19, and also of leg 17 and tube 19. A hydrocarbon-water interface is maintained in leg 17 at a level A which is below the lowest point in the junction of tube 19 and leg 17; how this is done will be explained hereinafter. -Any free water contained in the feed or sample hydrocarbon stream flows by way of tube 19 into leg 17, and settles out at the bottom of this leg, since the water is heavier or of higher density than the hydrocarbon. .The separator leg 17 (and also the branch tube 21, which communicates with tube 19 and with the separator leg 17) fills to the upper end of tube 22, which latter carries sample through the heat exchanger 3, 6 to the boiler 16 A vent tube 24 opens at its lower end into the space above the liquid level B of the hydrocarbon in separator leg 17, this tube extending upwardly and out through the wall of leg 17, and the upper end of such tube being open to the atmosphere. Tube 24 ensures that atmospheric pressure is maintained in leg 17, above the liquid level B therein. Since there is atmospheric pressure above the liquid level B of the hydrocarbon in leg 17, and since the upper end of branch tube 21 opens to the atmosphere, the liquid level B will normally be the same in both leg 17 and branch tube 21, and it is so illustrated in FIG. 2.

Because of the overflow pipe 6, the liquid hydrocarbon cannot rise (in boiler 16) above the upper open end of such pipe, a level denoted by C. There is atmospheric pressure above level C in boiler 16, and also above the liquid in tube 22. For convenience in illustration, the liquid is shown at the samet level C in both tube 22 and boiler 16. However, it will be appreciated that actually, during normal, continuous feed, the liquid in tube 22 would have to be somewhat above level C, to develop enough head to cause flow down through tube 22 and back up through tubular member 3 to the level C in boiler 1 As in FIG. 1, the sample is boiled by heat supplied by cartridge heater 5 in a well in the bottom of the boiler 16, producing some vapor. However, in FIG. 2 the boiling is made to take place rather rapidly, to reduce the time lag (due to the liquid being held up in the separator 17, on its way to the boiler) as much as possible.

A thermocouple 12, to which leads 13 are connected, is positioned in the vapor space above the liquid in boiler 16, to detect a vapor temperature in this boiler leg. Leads 13 extend upwardly to the top of leg 16, and out through a suitable seal (not shown) to a recording potentiometer 14. The position of the thermocouple 12 is critical, and must be determined experimentally (by comparison with the results of laboratory tests, using ASTM Method 13-86) to record the desired temperature, which in this case is the initial boiling point of the sample.

Vapor from the boiler 16 passes upwardly to the top of this leg, from whence it passes through arm 18 to leg 17. The upper part of leg 17, from a point slightly below the top of this leg to a point near the bottom thereof but above tube 19, is provided with a surrounding jacket 7 through which a cooling liquid such as water is circulated by means of the hose couplings 8 and 9 provided at the upper and lower ends, respectively, of jacket 7. The arrangement 7-9 comprises a water-jacketed condenser, which cools the wall of leg 17. Vapor from the boiler leg 16, which reaches separator leg 17 by way of the horizontally-disposed arm 13, is condensed in the condenser 79. The condensate flows down, along the inner wall of leg 17, to the water separator which is provided at the bottom of this leg. Water in the condensate (from dissolved water in the feed) settles to the bottom of the separator and helps form the water phase whose level (and thereby also the hydrocarbon-water interface) is indicated at A. Reflux to the boiler 16 takes place by way of 19, 21, 22, etc., the reflux flowing along with the original feed in 21 and 22.

One end of a water overflow tube or conduit 25 is coupled to the bottom of separator leg 17. Tube 25 extends upwardly from the bottom of leg 17 to a predetermined level D (determined as described hereinafter), at which level it is coupled to a downwardly-extending water drain tube 26. A vent tube 27, which extends upwardly from level D and from tube 26, is aligned with tube 26; tube 27 is open to the atmosphere at its upper end. It may be seen that, when the water level in overflow tube 25 rises above the junction of this tube with drain tube 26, the water will flow over into tube 26 and downwardly in the latter to a suitable waste or drain connection. Thus, separated water (separated in separator leg 17) can flow out the overflow tube 25 and drain tube 26.

The predetermined level D (previously referred to) of the tube 25 (i.e., the level at which tube 25 is joined to tube 26) must be adjusted to suit the density of the hydrocarbon sample, so that the hydrocarbon-water interface is maintained at A. The level at which this interface is maintained depends on the density of the hydrocarbon sample and the difference (denoted by Ah) be tween the levels B and D. The interface A will form at the level where h the head of hydrocarbon (i.e., the difference between the levels B and A), is balanced exactly by h the head of water (i.e., the difference between the levels D and A); this is true since atmospheric pressure is effective on both levels D and B. It should be realized that since the hydrocarbon is less dense than the water, 11 will exceed h by All.

Since the height of the interface A depends upon (among other things) Ah, the height of level D may be mechanically adjusted (as by means of a flexible tube) to vary the height of the interface A. The interface level must be maintained below the lowest point in the junction of tube 19 and leg 17, so that free water which enters tube 19 by way of tube 20 will drop down to level A and be held in the separator 17, rather than traveling to the boiler 16 along with the feed. Also,

the interface level must be maintained above the highest point in the junction of overflow tube 26 and leg 17, so that no hydrocarbon can enter the overflow tube 25.

A jacket 28 of heat insulating material surrounds the boiler leg 16, arm 18, and that portion of separator leg 16 which is above the water jacket 7. This prevents any appreciable cooling of any of these walls (and thus maintains them at a high temperature), thereby preventing the formation of any condensate in leg 16 or arm 18. Since the condensation is made to take place in the separator leg 17, and since condensation in leg 16 is eflectively prevented, there is no place in the boiler 16 where liquid water can accumulate, and thereafter find its Way back into the hot boiler. Thus, the upset of the apparatus by water (which takes place in FIG. 1, as previously described) cannot take place in the apparatus of FIG. 2. The water in the condensate is separated or removed (in separator leg 17) before the condensate refluxes to the boiler 16, and any free water in the feed is removed (by this same separator) before the feed reaches boiler 16.

In an actual test run of the FIG. 2 (continuous) analyzer, a wet plant sample of kerosene was fed to the device. During three days operation, the indicated vapor temperature (detected by thermocouple 12, and recorded on item 14) varied from 385 F. to 400 F., as a result of fluctuations in refinery plant operation. During this period, eight routine samples were distilled in the laboratory, using ASTM Method D-86. Five of the eight samples agreed with the continuous analyzer reading (on item 14, FIG. 2) within 1 F., one differed by 2, one by 3, and one by 5 F. No variations of temperature, attributable to water, occurred. These results are in sharp contrast to the results (set forth hereinabove) obtained on a test run using the FIG. 1 device.

FIG. 3 illustrates an alternative construction which utilizes the same principles of operation as FIG. 2, but wherein the tubing configuration for the feed to the boiler is modified somewhat. In FIG. 3, parts which are the same as those in FIG. 2 are denoted by the same reference numerals. In FIG. 3, a base or bottom closure 2 is provided on separator leg 17. One leg of a T-joint 30 is sealed into a suitable aperture provided in closure 29. A feed tube 31 extends coaxially through the two aligned arms of the T, by way of a sealed joint at the bottom of the T. The upper end of tube 31 extends into the interior of leg 17, this tube end being located above the hydrocarbon-water interface A. A sample of the wet liquid hydrocarbon stream is fed continuously into the separator leg 17, by way of feed tube 31. Any free water in the feed emerges from the upper end of feed tube 31, and, because it is higher in density than the hydrocarbon, settles out at the bottom of leg 17, to add to the water phase below interface A.

A tube or conduit 32 is sealed through closure 29, this tube acting as an overflow pipe to maintain the hydrocarbon at the desired level B. Conduit 32, like conduit 22 in FIG. 2, extends downwardly and horizontally from leg 17, to open into the tubular member 3 (not shown in FIG. 3), which forms part of a heat exchanger and the upper end of which opens into the boiler leg 16.

In FIG. 3, the separator leg 17 fills to the upper end of tube 32, when sample is fed into this leg by way of tube 31. The flow of sample to tube 32 takes place by way of a baflle 33, to be later described. Tube 32 then carries the sample through the heat exchanger into boiler leg 16, just as does tube 22 in FIG. 2. The upper end of tube 32 is located some distance above the upper end of tube 31.

In FIG. 3, the vessel end of the water overflow tube 25 is coupled directly to the horizontally-extending leg of the T-joint 30, this tube extending upwardly to a predetermined level D, just as in FIG. 2. The hydrocarbon-water interface A must be maintained above the horizontally-extending leg of T-joint 30. With the interface A at the level illustrated in FIG. 3, the entire T-joint 30 is filled with water, as is the water overflow tube 25, but there is only wet hydrocarbon feed in tube 31.

A piece 33 of tubing, open at both ends, surrounds but is spaced from tube 32. The lower end of tubing 33 rests on closure 29, to maintain such tubing in position in separator leg 17 while the upper end of this tubing is located above the hydrocarbon level B and above the upper end of tube 32. Above the hydrocarbon-water interface A, tubing 33 has therein a side port or aperture 34, through which liquid may enter this tubing.

Tubing 33 serves as a baffle, to control liquid flow. Condensate (resulting from the action of the water-jacketed condenser 7, etc.) flowing down the inner wall of leg 17 must flow downward around the outside of tubing 33 as far as port 34, and then through this port and up inside tubing 33, in order to reach the overflow pipe 32. This allows time for water in the condensate to coalesce, before the hydrocarbon refluxes to the boiler 16. The amount of water in the returning or refluxing liquid is therefore minimized. In this connection, it is pointed out that reflux to the boiler 16 takes place by way of conduit 32 (after passage through the baflle 33, as just described), the reflux flowing along with the original feed through conduit 32.

Without the bafile 33, condensate from the condenser 7, etc. could flow directly into the overflow pipe 32 before the water has completely separated from the hydrocarbon.

In FIG. 3, water is separated from the condensate, in leg 17, in substantially the same manner as in FIG. 2.

The invention claimed is:

1. Apparatus for analyzing a stream of liquid to determine the initial boiling point thereof, comprising a vessel having the general shape of an inverted U with two vertically-disposed legs and a horizontally-disposed arm, means for feeding the liquid stream to be analyzed to the first leg of said vessel at a point above the bottom thereof, a conduit coupled at one end to said first leg above said point and coupled at its other end to the second leg of said vessel, whereby the liquid stream to be analyzed may flow from said first leg into said second leg, means for heating said second leg to an elevated temperature to vaporize at least a portion of the liquid flowing thereinto, means for measuring a vapor temperature in said second leg, and means for cooling the wall of said first leg to condense the vapor reaching such leg by way of said arm.

2. Apparatus for continuously analyzing a stream of liquid to determine the initial boiling point thereof, comprising a vessel having the general shape of an inverted U with two vertically-disposed legs and a horizontally-disposed arm, means for continuously feeding the liquid stream to be analyzed to the first leg of said vessel at a point above the bottom thereof, a conduit coupled at one end to said first leg above said point and coupled at its other end to the second leg of said vessel, whereby the liquid stream to be analyzed may flow continuously from said first leg into said second leg, an overflow conduit connected to said second leg for draining off excess liquid which tends to accumulate therein, means for heating said second leg to an elevated temperature to vaporize at least a portion of the liquid flowing thereinto, means for continuously measuring a vapor temperature in said second leg, and means for cooling the wall of said first leg to condense the vapor reaching such leg by way of said arm.

3. Apparatus for analyzing a stream of liquid to determine the initial boiling point thereof, comprising a vessel having the general shape of an inverted U with two vertically-disposed legs, means for feeding the liquid stream to be analyzed to the first leg of said vessel at a point above the bottom thereof, a conduit coupled at one end to said first leg above said point and coupled at its other end to the second leg of said vessel, whereby the liquid stream to be analyzed may flow from said first leg into said second leg, means for heating said second leg to an elevated temperature to vaporize at least a portion of the 7 liquid flowing thereinto, and means for measuring a vapor temperature in said second leg.

4. Apparatus for analyzing a stream of liquid to determine the initial boiling point thereof, comprising a vessel having the general shape of an inverted U with two vertically-disposed legs, means for feeding the liquid stream to be analyzed to the first leg of said vessel at a point above the bottom thereof, a conduit coupled at one end to said first leg above said point and coupled at its other end to the second leg of said vessel, whereby the liquid stream to be analyzed may flow from said first leg into said second leg, a tube coupled at one end to the bottom of said first leg and free at its other end, said other end of said tube extending upward with respect to the bottom of said first leg, means for heating said second leg to an elevated temperature to vaporize at least a portion of the liquid flowing thereinto, and means for measuring a vapor temperature in said second leg.

5. Apparatus for continuously analyzing a stream of liquid to determine the initial boiling point thereof, comprising a vessel having the general shape of an inverted U with two vertically-disposed legs, means for continuously feeding the liquid stream to be analyzed to the first leg of said vessel at a point above the bottom thereof, a conduit coupled at one end to said first leg above said point and coupled at its other end to the second leg of said vessel, whereby the liquid stream to be analyzed may flow continuously from said first leg into said second leg, an overflow conduit connected to said second leg for draining off excess liquid which tends to accumulate therein, means for heating said second leg to an elevated temperature to vaporize at least a portion of the liquid flowing thereinto, and means for continuously measuring a vapor temperature in said second leg.

6. Apparatus for continuously analyzing a stream of liquid to determine the initial boiling point thereof, comprising a vessel having the general shape of an inverted U with two vertically-disposed legs, means for continuously feeding the liquid stream to be analyzed to the first leg of said vessel at a point above the bottom thereof, a conduit coupled at one end to said first leg above said point and coupled at its other end to the second leg of said vessel, whereby the liquid stream to be analyzed may flow continuously from said first leg into said second leg, an overflow conduit connected to said second leg for draining off excess liquid which tends to accumulate therein, a tube coupled at one end to the bottom of said first leg and free at its other end, said other end of said tube extending upward with respect to the bottom of said first leg, means for heating said second leg to an elevated temperature to vaporize at least a portion of the liquid flowing thereinto, and means for continuously measuring a vapor temperature in said second leg.

7. Apparatus as set forth in claim 6, wherein the firstmentioned conduit and the overflow conduit are in ther mal contact with each other, thereby to cause heat exchange between the liquid flowing into said second leg and the said excess liquid.

8. Apparatus for continuously analyzing a stream of liquid to determine the initial boiling point thereof, comprising a vessel having the general shape of an inverted U with two vertically-disposed legs and a horizontally-disposed arm, means for continuously feeding the liquid stream to be analyzed to the first leg of said vessel at a point above the bottom thereof, a conduit coupled at one end to said first leg above said point and coupled at its other end to the second leg of said vessel, whereby the liquid stream to be analyzed may flow continuously from said first leg into said second leg, an overflow conduit connected to said second leg for draining off excess liquid which tends to accumulate therein, a tube coupled at one end to the bottom of said first leg and free at its other end, said other end of said tube extending upward with respect to the bottom of said first leg, means for heating said second leg to an elevated temperature to vaporize at least a portion of the liquid flowing thereinto, means for continuously measuring a vapor temperature in said second leg, and means for cooling the wall of said first leg to condense the vapor reaching such leg by way of said arm.

References Cited in the file of this patent UNITED STATES PATENTS 1,079,398 Coakley et a1 Nov. 25, 1913 2,594,683 Rolfson Apr. 29, 1952 2,986,279 Henigman May 30, 1961 OTHER REFERENCES Garvitch: In Journal of Scientific Instruments, vol. 32, July 1955 (pages 261, 262). 

1. APPARATUS FOR ANALYZING A STREAM OF LIQUID TO DETERMINE THE INITIAL BOILING POINT THEREOF, COMPRISING A VESSEL HAVING THE GENERAL SHAPE OF AN INVERTED U WITH TWO VERTICALLY-DISPOSED LEGS AND A HORIZONTALLY-DISPOSED ARM, MEANS FOR FEEDING THE LIQUID STREAM TO BE ANALYZED TO THE FIRST LEG OF SAID VESSEL AT A POINT ABOVE THE BOTTOM THEREOF, A CONDUIT COUPLED AT ONE END TO SAID FIRST LEG ABOVE SAID POINT AND COUPLED AT ITS OTHER END TO THE SECOND LEG OF SAID VESSEL, WHEREBY THE LIQUID STREAM TO BE ANALYZED MAY FLOW FROM SAID FIRST LEG INTO SAID SECOND LEG, MEANS FOR HEATING SAID SECOND LEG TO AN ELEVATED TEMPERATURE TO VAPORIZE AT LEAST A PORTION OF THE LIQUID FLOWING THEREINTO, MEANS FOR MEASURING A VAPOR TEMPERATURE IN SAID SECOND LEG, AND MEANS FOR COOLING THE WALL OF SAID FIRST LEG TO CONDENSE THE VAPOR REACHING SUCH LEG BY WAY OF SAID ARM. 